The present invention relates to a mechanism for actuating a switch and transmitting force or motion to a system component. It finds particular application in conjunction with actuating a lost motion switch and transmitting force or motion to a system component while allowing angular articulation of at least one component of the mechanism and will be described with reference thereto. It will be appreciated, however, that the invention is also amendable to other applications.
As is known in the art, many types of systems utilize a mechanism, linkage, or the like to transmit motion and/or force to or from the system. In some systems, it is desirable to initially actuate a switch prior to transmitting the force or motion. For example, in passenger cars and heavy vehicles, the brake lights and cruise control cutoff are actuated by a very small amount of initial brake pedal travel, which is typically solely designed to actuate the switch. The switches used for these applications are termed “lost motion” switches.
FIG. 1 illustrates a known design for a lost motion switch 10. The switch 10 includes a body 12 which houses electrical contacts (not shown) and has an integral electrical connector 14. The switch 10 also includes a plunger 16 that extends from the body 12. When the plunger 16 is depressed into the body 12, typically against the bias of an internal spring (not shown), the electrical contact of the switch 10 change from a first state to a second state, such as for example from a closed state to open state or vice versa. The plunger 16 is located between two mounting ears 18a, 18b. Each ear 18a, 18b, includes an opening 20a, 20b for mounting the switch 10.
FIGS. 2 and 3A–B illustrate a known mechanism 22 for actuating a lost motion switch 10 in a vehicle brake application. In addition to actuating the lost motion switch 10, the mechanism transmits motion from a brake pedal arm 24 to the brake system. The switch 10 typically mounts onto a pin 26 via the openings 20a, 20b in the ears 18a, 18b (see FIG. 1). The pin 26 also mounts to the pedal arm 24 and through an opening 28 in a connecting member 30, such as for example a yoke or pushrod. The mechanism 22 is designed such that movement of the pedal arm 24 results in movement of the yoke 30. Movement of the yoke 30 actuates the brake system component (not shown), such as a brake valve, in an air-braked vehicle or a master cylinder, or a hydraulic brake booster, such as for example a Hydroboost® or Hydromax®, in a hydraulically braked vehicle.
The lost motion switch 10 is positioned to straddle the yoke 30. The yoke 30 includes a nose portion 32 which mates with and depresses the lost motion switch plunger 16 during brake pedal actuation. This occurs because the pin 26 is sized to fit snugly through the openings 20a, 20b in the mounting ears 18a, 18b (see FIG. 1) while having clearance in the opening 28 in the yoke 30. In particular, as the pedal arm 24 moves in response to a user depressing the brake pedal (not shown), the pin 26 is forced from one side of the opening 28 in the yoke to the other side (see FIGS. 3A–3B). This results in the nose 32 depressing the switch plunger 16 and actuating the switch 10. As the pedal arm 24 continues to travel, the pin 26 engages the opposite side of the opening 28 and motion of the pedal arm is then transmitted through the braking system.
In some applications, however, the known mechanism of FIGS. 1–3 is ineffective. For example, the brake systems of low cab forward/low front entry vehicles have space constraints that may require motion from the pedal arm 24 to be redirected transverse to the direction movement of the arm. As a result, the yoke 30 may have side-to-side motion relative to the pedal arm 24 and lost motion switch 10. Lost motion switches, however, are designed for and best suited to operate when the components of the mechanism all move along a single direction or single/parallel plane(s). In these applications, motion of the yoke 30 that is transverse to the motion of the switch can cause the switch to be less reliable and fail prematurely.